The present invention relates to a recording medium, a method for the preparation of a recording medium, and a coating composition useful in the preparation of a recording medium.
A surface coating is sometimes applied to a recording medium in order to improve its printing properties. For example, the coating can improve the appearance, ink absorption, and/or image smear resistance of the medium.
Surface coatings can be classified into two general categoriesxe2x80x94glossy coatings and non-glossy (matte or dull) coatings. Glossy coatings are often desirable, as they are very smooth, and can impart a superior feel and a photograph-like quality to a recorded image.
A coating composition comprising a pigment such as a hydrated aluminosilicate (such as a kaolin clay), titanium dioxide, alumina, silica, or calcium carbonate can be used to make a glossy coating if the composition is applied by cast coating, wherein the composition is dried while contacting a polished metal cylinder or drum (e.g., a polished chromium drum). A glossy pigment coating prepared in this manner is advantageous not only for its gloss, but because the pigment can impart a relatively high rate and capacity of ink absorption to the coating as well. However, the cast coating procedure is relatively slow and costly.
It is possible to make glossy pigment coatings using application methods which are cheaper and faster than cast coating (e.g., bar coating, air-knife coating, roll coating, etc., sometimes followed by calendering), but the overall gloss of the resulting coating is often diminished compared to cast coating. Moreover, glossy pigment coatings prepared using these rapid, inexpensive methods also can be quite brittle, and the coatings often crack and flake upon drying.
Coating compositions comprising resins such as polyolefin resin, polyester resin, polyamide resin, or polycarbonate resin can be applied using the aforementioned rapid, inexpensive coating methods (e.g., bar coating, air-knife coating, roll coating, etc.), to form coatings having a high gloss. However, a recording medium having such a glossy resin coating generally has significantly decreased rates of ink absorption and ink drying compared to a recording medium having a pigment coating.
A need exists for a recording medium having a glossy coating that can be applied using a rapid, inexpensive coating procedure, wherein the glossy coating is non-brittle, and wherein ink applied to the recording medium is rapidly absorbed, and rapidly dries. A need also exists for a method of preparing such a glossy recording medium, and for a coating composition that can be used in such a method. The present invention provides such a recording medium, method, and composition.
The recording medium of the present invention comprises a substrate having a glossy coating thereon, wherein the glossy coating comprises first and second groups of particles, wherein:
(a) the first group comprises metal oxide particles, wherein the metal oxide particles are aggregates of smaller, primary particles,
(b) the mean diameter of the primary particles is less than about 100 nm,
(c) the mean diameter of the aggregates is from about 100 nm to about 500 nm,
(d) the mean diameter of the particles in the second group is less than about 50% of the mean diameter of the aggregates in the first group, and
(e) the ratio of particles in the first group to particles in the second group is from about 0.1:1 to about 10:1 by weight.
The coating composition of the present invention comprises a suitable carrier and first and second groups of particles, has a solids content of at least about 15% by weight, has an apparent viscosity at a relatively high shear rate of less than about 100 centipoise at 22xc2x0 C., and can be applied to a substrate to form a substrate having a glossy coating thereon.
The inventive method of preparing a recording medium comprises: (a) providing a substrate, (b) coating the substrate with the coating composition of the present invention to provide a coated substrate, and (c) drying the coated substrate to form the recording medium.
The recording medium of the present invention comprises a substrate having a glossy coating thereon, wherein the glossy coating is non-brittle and crack-resistant, has an excellent rate of liquid absorption, has a relatively high liquid absorption capacity, has excellent adhesiveness, and can be applied using rapid, inexpensive coating methods. These and other advantages of the present invention, as well as additional inventive features, will be apparent from the description of the invention provided herein.